When a scene is filmed in the production of a feature motion picture film, a sound recording of dialogue and sound effects is made on 1/4 inch tape using a high quality tape recorder. This tape is re-recorded onto magnetic tape having sprocket holes along the length thereof of the same size and format as the picture film. In the industry, such magnetic tape is termed magnetic film or "mag" film. By use of magnetic film, synchronization between sound tracks and picture film may be readily maintained during the picture and sound editing processes.
Sound editing generally involves editing of dialogue, effects and music, each of which may be recorded on one or more magnetic films. For example, a separate reel of magnetic film is made for each actor's lines so that the level of each may be separately set. Thus, at the end of actor A's first line on a reel, the film is cut; this will become the "element" for A's dialogue. Actor B's element must be restored to the same length from the start mark as the original track, so an identical length of "fill" stock is spliced in ahead of B's first line. Now, if both reels are started from the beginning, and run synchronously, both actors' lines will be spoken at precisely the same moment in time as they were in the original recording. More fill is spliced onto the end of A's first line to make up for B's dialogue, and the process is continued to the end of the reel, so that two separate elements have been constructed, giving separate control over each.
At this stage, the jobs of effects editors and music editors are similar in concept to cutting dialogue; elements are built from individual effects or pieces of music. But none of them ends here: now qualitative judgements as to the useability of the tracks must be made. If B's first line was not delivered to the director's satisfaction, then dialogue replacement tracks will be made in a studio where the actor watches the scene while listening to his original dialogue on headphones. The whole scene is "looped", so that it runs over and over, and each time it goes by the actor can deliver the line again and have it recorded. The process is called Automatic Dialogue Replacement, or ADR.
These ADR tracks go to the dialogue editor, who may discard some as useless, and construct new elements of the rest, so that the director and sound mixer can select the take they want in the context of a rough mix of dialogue, effects and music. Their selection goes back to the cutting room to replace the offending line of the original element.
A new problem now arises: The background sounds of the original scene were not present in the ADR studio, so that if the ADR line is used as is, there will be a distracting loss of background or "atmosphere" during that line. Since there is no way to separate the original background atmosphere from the bad line, the editor must somehow reconstruct the atmosphere and merge it in, mix it, with the ADR line to make it sound similar enough to the original that a difference will not be noticeable or distracting. This might be done by reproducing a section of the original track with no dialogue or other non-atmosphere sound, or by construction of a whole separate atmosphere element for the scene using tapes from the sound library. Either way, the editor has a new element, a separate reel labeled "atmosphere". The level on this element is far lower than the dialogue or effects; it must be mixed in carefully in the studio to match exactly the other atmosphere. Music and effects editing each have their peculiar complexities and nuances; but, they are similar to dialogue in that all three involve the creation of many elements and the detection and elimination of all possible flaws.
Each track becomes a complete, separate reel of magnetic film the identical length of the picture reel and synchronized to it. Their common destination is the mixdown theatre, which contains a motion picture projector and a number of magnetic film transports (dubbers) for the sound, which can be run in absolute synchronization with the picture projector. The sound mixer, whose responsibility is the final sound of the film, has a mixing console which enables him to adjust the level and tone (equalization) of each track, as well as overall loudness. He listens to his work on a high quality sound system capable of high sound levels and full frequency reproduction of all tracks; any sound present on those tracks will be heard and is subject to detailed scrutiny. Additional audio processing equipment such as graphic equalizers, time delays, compressors, and the like, is available for use on any track or element the mixer desires. Pops, clicks, abrupt transitions, and other extraneous background noise not detected and eliminated by the sound editor are detected in the mixdown theatre by the sound mixer, and will be sent back to the sound editor for correction.
Equipment for use by sound editors includes an editorial bench with shelves at the rear for reels of film and miscellaneous supplies. At the left and right ends of the bench, on the front, are two hand-crank film rewinds. A reel of film is loaded onto one rewind, and an empty reel onto the other. The film is threaded onto the empty reel and wound onto it by turning the crank.
On the way from one reel to another, the film usually passes through a synchronizer; this is a device which has several sprocket wheels which can propel, or be turned by, the film. The wheels all attach to a common horizontal shaft and a mechanical footage counter, and can be driven with a handle at the front of the unit. Film sits flat as it traverses the synchronizer, so that the picture can be scrutinized from above. A spring-loaded gate with guide rollers is pushed down and locked on top of the film to keep the sprocket holes in the film engaged with the teeth on the wheel. Other sprocket wheels of the synchronizer are used to drive magnetic film in synchronization with the picture film. A spring-loaded gate with guide rollers is associated with each of these sprocket wheels to maintain the magnetic film in engagement with the teeth on the wheels. A magnetic tape playback, or pickup, head is attached to a pivotally mounted arm carried by the magnetic film gates for pivotal movement of the heads into and out of engagement with the associated magnetic film. A typical synchronizer comprises a track for the picture film and three or four tracks with playback heads for magnetic film.
Cables from the playback heads of the synchronizer plug into a sound reader comprising a signal mixer and amplifier termed a "squawkbox" in the trade. Separate level controls are provided for signal level control of the low-level signals from the pick up heads at the sound reader.
A film splicer and grease pencils for marking the tracks complete the compliment of equipment of the editing bench.
Off to one side of the bench, on the floor, an upright editing machine often is provided, which is used to magnify the picture for viewing and to run the film at standard film speed. It contains a sound track reader for magnetic film, and a self-contained preamplifier, amplifier and speaker. A monaural headphone jack is provided. A magnetic tape playback head is mounted on a hinged arm on top of a film gate, similar to the pick up head mountings included in the synchronizer. The upright editing machine generally includes a good projector movement, but it is not acoustically isolated, and so it is quite noisy. The sound editor uses this machine to synchronize sound tracks to the picture, to determine whether sounds on the track occurred on or off camera, to audition tracks against the picture, and generally for any task requiring close viewing of the film.
The mechanical, electronic, and operational problems inherent in editorial devices are many and of the sorts which conspire to make difficult the job of building elements, judging their quality, and cleaning them up for the mix. Signals from tape playback heads are very small and must be amplified several orders of magnitude to be useful. In the cutting room these signals lead a perilous life.
A tape splicer can become magnetized, leaving a click or pop on the track at every splice. These can be virtually inaudible on the cutting bench equipment, yet quite obvious in the mixdown theatre, for reasons detailed below.
The alignment of tape heads on professional equipment is critical; a few thousandths of an inch misalignment can result in an order of magnitude or more of signal loss across the audio spectrum or in high frequency response. The mounting of heads on synchronizers and upright editing machines was not designed for precision but for ease of film handling, and the more the heads are flung out of the way, the worse the alignment becomes. Consequently, anything which reduces the moving of heads is desirable.
In studio tape transports, leads from tape heads are kept as short as possible, and heavily shielded to minimize pickup of hum, motor noise, etc. On the editorial bench, leads from synchronizer to sound reader may be several feet long and terminated in unshielded plugs. Any nearby source of hum, or noise, such as the AC power cord for the sound reader, which is usually plugged into the convenience outlet at the back of the bench, will be picked up and amplified.
The metal boxes into which sound readers are built are usually considered sufficient shield against external electromagnetic radiation, and the internal wiring of the tape leads is left unshielded. This results in several problems: the unit's own power transformer and rectifier can induce a strong hum, which at high levels of amplification can literally drown the audio signal; stray capacitance and inductance effects cause spurious oscillation, usually a high-pitched squeal that happens when the volume is turned up more than 60 or 70 percent. The presence in the box of a speaker, which draws a fair amount of current, can increase the problem to a point where it cannot be solved without resorting to elaborate and expensive electromagnetic shielding techniques. Most existing devices have at least one of these problems, and little has been done to correct them.
The speakers built into the sound readers are usually low quality; and the principles of acoustics seem to indicate that a small, undamped, unsealed metal box is hardly a good speaker cabinet. The frequency response is limited to midrange and any low bass or high treble sounds, such as pops, bumps of the microphone, generator motor noise, and wind noise, cannot be heard on the sound reader speaker, but will be heard (sometimes with a vengeance) in the mix theatre's full-range system.
Tape playback heads are a reactive electronic component; their output level and frequency response are sensitive to the electronic load presented to them. Prior art sound readers sum the low level playback head signals together passively into a single tape preamplifier. A passive summing network has a major drawback for a low-level signal such as this: in a properly designed summing network each time the number of inputs doubles, the level from any one input decreases by half, even if some inputs are unused. If the network is improperly designed, the tape heads serve as loads for each other; one head alone would be fine, but if two or more are connected, they each load the others, and now the load is reactive, with the resultant degradation of frequency response piled on top of the signal loss. In both cases the signal to noise ratio suffers, since the noise output of the circuit is constat while the input signal has been reduced.
Level control for individual channels is done by further attenuating the input signal; this further degrades the signal to noise ratio. For the editor all of this means that very low level signals are buried under hum and hiss, and they simply give up the ability to mix in favor of simply being able to hear.
As mentioned earlier, the upright editing machine is loud when picture is running. In a small untreated editing room the sound must be turned up quite loud to overcome it, or else the editor must use headphones. Use of headphones with the upright editing machine has a peculiar pitfall: the amplifier has a fairly high electronic noise floor, which, although adequate for the speaker, causes a problem for the headphones. Most headphones are so sensitive that the small voltage required to drive them forces the upright editing machine amplifier to operate annoyingly near its noise floor.
The results of all the above problems are that high quality location sound tracks are seriously degraded and distorted in the cutting room. If the process simply involved synchronizing the tracks to the picture, this might be acceptable; but, since the editors have the greater problem of matching low level atmospheres and finding low level flaws, it becomes evident that their equipment is far from ideal.
If the editorial environment is considered as a system whose product is destined for high-technology mixdown theatre, some extra operational problems can be noted.
In the selection of tracks it is frequently desirable to be able to mix different tracks to appropriate levels, in order to tray a "scratch mix," to see how the effect or music will sound in the context of the rest of the sound track. At times it is necessary to mute some tracks or to solo one. With existing devices this is done either by reducing the level on the particular track or tracks to zero (thereby losing preset levels for those tracks) or by lifting the tape heads off the unwanted tracks (hastening the misalignment of the tape heads).
The use of headphones precipitates some other problems:
a. Existing editorial devices come equipped with a monaural headphone jack. All decent quality headphones which are readily available today are stereophonic, and when plugged into a monaural jack they receive sound on one earpiece only. The purchase of a mono-stereo adaptor currently solves this problem. PA1 b. When the editor decides to change from the sound reader to the upright editing machine, he has to unplug the headphones from the "squawkbox" at the back of the bench, disentangle the cord from the tracks, and plug it into the upright editing machine; or else use two sets of headphones and switch between the two. (The latter can be ludicrous with the entanglement of cords, tracks, and film. In fact it is not an efficient way to work.) PA1 c. Music and effects cutters sometimes like to use a 1/4 inch stereo tape deck handy to audition potential tracks. This practice saves them trips to the sound effects library or time spent waiting for transfers to be made, and it allows then to audition effects against the picture. In order to try them in context, however, they have to listen to the audition track over headphones or a stereophone speaker system while hearing the remainder over the upright editing machine speaker. This is a crude way of mixing, since the track from the upright editing machine has to be loud enough to overcome the film clatter, and the tape deck may not drive headphones very loud. A real audition is not possible in the cutting room, and often the track to be auditioned must be transferred to magnetic film, taken to the mix theatre, and put up with picture and the rest of the sound track. A lot of time and film is wasted in the process. An additional annoyance for headphone users is that the monoaural adaptor has to be unplugged to use the phones with the stereophonic tape deck.
Some contemporary sound editors have taken to using an external stereophonic amplifier and speakers to supplement their editorial systems, particularly for effects and music cutting. They quickly encounter the problem that none of the old editing room equipment is designed to interface with a modern audio system; piles of equipment quickly grow up on the back of the bench in the attempt to deal with the interface problem, taking up work space and hindering the physical efficiency of the bench.
Even with the successful interface of the stereo system, the problem still remains that the equipment is still too spread out to be operated conveniently from one location. The editor constantly has to lean over the bench or turn around to get at the appropriate control, and he still loses some of the efficiency originally intended in the bench arrangement.